Quantum optics
Can a strain-tuned quantum dot make an ideal single-photon source?
Open access · cc by · source: Europe PMC
A quantum dot built into a tiny curved-mirror cavity on a piezoelectric base can be squeezed into resonance and then emits bright, nearly perfect single photons.
Study at a glance
- Design
- Other — Fabrication and optical characterisation of a single InAs quantum dot deterministically placed in a Fabry-Perot microcavity on a piezoelectric actuator, with FDTD design simulations.
- N
- No sample N; photon statistics reported for one device, with Q-factor trends averaged over several cavities per defect size.
- Population
- InAs/GaAs quantum dots in monolithic dielectric/semiconductor Fabry-Perot microcavities on PMN-PT
- Outcome
- Cavity Q factor, strain tuning range, Purcell factor, extraction efficiency, single-photon purity g2(0), and HOM indistinguishability
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Key findings
Cavity quality rose with defect width to a plateau near a Q of about 15,000, and strain tuned the dot by about 1.3 nm with the cavity mode staying put, giving roughly 50-fold brighter emission on resonance. The coupled dot's lifetime shortened to about 100 ps, a Purcell factor of about 9, with an extraction efficiency of 0.58. Single-photon purity was high, with g2(0) of 0.044, and corrected indistinguishability was 0.922.
Methodology
The team grew quantum dots inside a semiconductor mirror structure, located individual dots by fluorescence imaging, and built a small lens-shaped silica bump above each one topped by a dielectric mirror, forming a Fabry-Perot microcavity. The thin membrane was transferred onto a piezoelectric crystal, so a voltage could strain the dot and shift its emission colour into resonance with the cavity. They then measured cavity quality, tuning, emission lifetime, brightness, photon antibunching and two-photon interference.
Limitations
The headline photon statistics come from a single device, so yield and device-to-device variation are not established. Measured Q factors fell short of simulations, which the authors attribute to imperfect evaporated dielectric layers and surface losses; the simulated extraction efficiency of 94.9% was not reached. The indistinguishability figure is corrected for setup imperfections (raw visibility was lower), and the tuning range is only about a nanometre.
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